1. Field of the Invention
The instant invention generally relates to an improved process for producing bis-(morpholino-N-alkyl) ethers directly from the corresponding N-(hydroxyalkyl)-morpholine compound; and more particularly, to an improved liquid phase process for selectively producing bis-(morpholino-N-alkyl) ethers in the presence of certain specific catalytically effective substances.
2. Prior Art
Bis-(morpholino-N-alkyl) ethers are generally well-known compounds having established utility as polyurethane catalysts. Generally the entire class of these compounds is useful in catalyzing urethane systems including the C-alkyl substituted bis-(morpholino-N-alkyl) ether compounds wherein one or both of the morpholine moieties contain C-(substituted) alkyl radicals on one or more of the carbon atoms and/or wherein the N-alkyl moiety is either a branched or straight chain radical containing from 1 to about 10 carbon atoms.
Bis-(morpholino-N-alkyl) ethers have been prepared by many methods. Examples of some of the more well-known methods are disclosed in U.S. Pat. No. 3,787,354. In on method for DMDEE synthesis, N-(2-chloroethyl)morpholine is reacted with N-(2-hydroxyethyl)morpholine (HEM) and sodium. See, for example, J. Amer. Chem. Soc., 62, 1448 (1940) and Aeta Chem. Scand., 8, 350 (1954). Another method involves the reaction of triethanolamine in the presence of hydrochloric acid. See, for example, J. Pharm. Soc. Japan, 75, 1367 (1955). Still another method involves the reaction of morpholine with bis-(2-chloroethyl)ether. See, for example, Bull. Soc. Chim. France, 3537 (1965). Many of these processes involve caustic neutralization with attendant problems or require the use of excess reagents to react with liberated chlorine compounds. In addition, these methods involve the use of difficulty obtainable chemical intermediates such as raw materials and/or produce the desired product in low yield wherein the reaction product mixture contains by-products which are difficult to separate by known methods.
Another method involves the vapor phase reaction of N-(2-hydroxyethyl)morpholine (HEM) in the presence of an activated alumina catalyst to form DMDEE. See, for example, J. Amer. Chem. Soc., 63, 298 (1941). This method suffers the attendant problems of vapor phase synthesis with low yields and extensive by-product formation.
Unexpectedly it has been found that bis-(morpholino-N-alkyl) ethers can be selectively produced directly from the readily available corresponding N-(hydroxyalkyl)morpholine in liquid phase without the attendant deficiencies of previously known processes. Under rigorous reaction conditions, i.e. temperatures in the 200.degree. C to 300.degree. C range, the inventive process is surprisingly selective to the desired product. The expected extensive decomposition and concomitant production of unwanted side products is minimized. Additionally, the compounds effective in catalyzing the synthesis of the instant invention are readily available. Another outstanding advantage resides in the fact that the most prevalent by-product of the instant process is the corresponding N,N'-dimorpholino-.alpha.,.omega.-alkane. While the production of this by-product is insubstantial, i.e. from 1:10 to 1:20 or higher with respect to the desired product, it need not be removed from the final product. These N,N'-dimorpholino-.alpha.,.omega.-alkane compounds are non-deleterious to urethane systems and in fact act as a co-catalyst with the bis-(morpholino-N-alkyl) ethers for polyol-isocyanate reactions.